Generation of oxodiazonium ions 3.* Synthesis of [1,2,5]oxadiazolo[3, 4-c]cinnoline-1,5-dioxides

Article abstract of DOI:10.1007/s11172-011-0311-8

A reaction of 4-(N-nitramino)-3-phenylfuroxane with the Ac ₂O/H₂SO₄ system leads to the formation of [1,2,5]oxadiazolo[3,4-c]cinnoline-1,5-dioxide, the first representative of furox-anocinnolines. The reaction presumably proceeds through the transformation of the nitramine fragment NHNO₂ to the oxodiazonium ion [N=N=O] ⁺ with subsequent intramolecular attack by this cation on the phenyl ring. Furoxanocinnoline is also formed in the reaction of the 4-(N-nitr-amino)-3-phenylfuroxane O-methyl derivative with H₂SO ₄. It is assumed that this reaction also proceeds with involvement of the intermediate cation [N=N=O]⁺ formed by the protonation of the N=N(O)OMe group and subsequent elimination of MeOH. 7-Nitro derivative is formed when furoxanocinnoline is nitrated with the concentrated HNO₃/H ₂SO₄ mixture. The compounds obtained were characterized by ¹H, ¹³C, and ¹⁴N NMR spectroscopy.

Full text of DOI:10.1007/s11172-011-0311-8

Russian Chemical Bulletin, International Edition, Vol. 60, No. 10, pp. 2046—2050, October, 2011
2046
Generation of oxodiazonium ions
3.* Synthesis of [1,2,5]oxadiazolo[3,4ꢀc]cinnolineꢀ1,5ꢀdioxides
V. P. Zelenov, A. A. Voronin, A. M. Churakov, M. S. Klenov, Yu. A. Strelenko, and V. A. Tartakovsky
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Eꢀmail: churakov@ioc.ac.ru
A reaction of 4ꢀ(Nꢀnitramino)ꢀ3ꢀphenylfuroxane with the Ac2O/H2SO4 system leads to the
formation of [1,2,5]oxadiazolo[3,4ꢀc]cinnolineꢀ1,5ꢀdioxide, the first representative of furoxꢀ
anocinnolines. The reaction presumably proceeds through the transformation of the nitramine
fragment NHNO2 to the oxodiazonium ion [N=N=O]+ with subsequent intramolecular attack by
this cation on the phenyl ring. Furoxanocinnoline is also formed in the reaction of the 4ꢀ(Nꢀnitrꢀ
amino)ꢀ3ꢀphenylfuroxane Oꢀmethyl derivative with H2SO4. It is assumed that this reaction also
proceeds with involvement of the intermediate cation [N=N=O]+ formed by the protonation
of the N=N(O)OMe group and subsequent elimination of MeOH. 7ꢀNitro derivative is formed
when furoxanocinnoline is nitrated with the concentrated HNO3/H2SO4 mixture. The comꢀ
pounds obtained were characterized by 1H, 13C, and 14N NMR spectroscopy.
Key words: Nꢀnitramines, furoxanes, cinnolines, oxodiazonium ion, nitration, 1H, 13C,
14N NMR spectroscopy.
Nitric oxide (NO) is an important physiological regꢀ
the Ac2O/H2SO4 system,1 as well as by the reaction of
3ꢀ[methoxy(oxido)diazenyl]ꢀ4ꢀphenylfurazane with acids9
(Scheme 1). The reaction presumably proceeds via
the intermediate oxodiazonium ion
[N=N=O]+.
In the present work, these approachꢀ
es were used for the synthesis of furꢀ
oxanocinnolineꢀ5ꢀoxide (FCO) 2.
ulator of cardiovascular, immune, and nervous systems
(see, for example, review 2). Several classes of organic
compounds capable of forming NO in living organisms
are known. Benzofuroxane derivatives3,4 belong to one of
these classes. Immunodepressants,5 substances displaying
antileukemia activity,5 and vasodilators6—8 are found
among them. The purpose of the present work is to synꢀ
thesize new annulated furoxanes, potential NOꢀdonors.
Earlier, we have reported on the development of approꢀ
aches to the preparation of furazanocinnolineꢀ5ꢀoxide 1
by the reaction of 3ꢀ(Nꢀnitramino)ꢀ4ꢀphenylfurazane with
Synthesis of the starting compounds.
Nitramine 3 and its Oꢀmethyl derivative 4
are the starting compounds for the synꢀ
thesis of FCO 2 (Scheme 2). Note that before our work,
Scheme 1
For Part 2, see Ref. 1.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2009—2013, October, 2011.
1066ꢀ5285/11/6010ꢀ2046 © 2011 Springer Science+Business Media, Inc.

Oxodiazonium ion generation
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 10, October, 2011
2047
Scheme 2
i. HNO3 (70%), NH4NO3 (20%), H2O (10%), 10 °C, 1 h.
no furoxanes containing a primary nitramine group were
known.
(CDCl3, δN –52), resonating in the regions characterisꢀ
tic of these classes. The signals for the N→O group of
the furoxane ring in these compounds are very broad
(Δν1/2 > 500 Hz).
Synthesis of [1,2,5]oxadiazolo[3,4ꢀc]cinnolineꢀ1,5ꢀdiꢀ
oxides. The reaction of the Naꢀsalt 7 with the Ac2O/H2SO4
system leads to the formation of FCO 2 in 89% yield
(Scheme 3).
Apparently, the process proceeded through the interꢀ
mediate 8 with the subsequent reaction of the oxodiazoniꢀ
um ion with the benzene ring.
Compound 2 can be obtained directly from aminoꢀ
furoxane 5 (see Scheme 3). An equimolar amount
of HNO3 was added to a solution of aminofuroxane 5
in Ac2O, followed by immediate addition of a soluꢀ
tion of H2SO4 (1 equiv.) in Ac2O. Initially, formation
of nitramine 3 was observed, followed by a gradual
Nitration of 4ꢀaminoꢀ3ꢀphenylfuroxane (5) with 70%
HNO3 according to the method developed for the syntheꢀ
sis of nitramines of the furazane series10 led to nitramine
3, which contained a large amount of impurities. Considꢀ
erably better results were obtained for the nitration with
the HNO3/NH4NO3/H2O system. The nitrating mixtures
containing 68, 17, and 15% or 70, 20, and 10% of HNO3,
NH4NO3, and H2O, respectively, were used for the nitraꢀ
tion. In the first case, the nitration was carried out at
25 °C for 2 h, in the second case, at 10 °C for 1 h. In both
cases, the yields of nitramine 3 (64—76%, calculated on
the Naꢀsalt) were approximately the same. The reaction
product was dissolved in diethyl ether and dried with
MgSO4. According to the TLC data (AcOEt—light petrꢀ
oleum, 1 : 3), this solution contains nitramine 3, some
unreacted starting compound 5, and unidentified impuriꢀ
ties. A solution of nitramine 3 in Et2O can be stored in
refrigerator for several hours.
Nitramine 3 in the solid state is unstable: at room
temperature it rapidly decomposes with the formation
of several unidentified products. The reaction of nitrꢀ
amine 3 solutions and diazomethane in diethyl ether
leads to a mixture of Oꢀ and Nꢀmethyl derivatives 4 and 6
in the ratio 59 : 41, respectively (1H NMR spectroscopic
data). The reaction of the ethereal solution of 3 with
the solution of NaOH in MeOH gives Naꢀsalt 7 (see
Scheme 2).
accumulation of cinnoline
2 (TLC monitoring,
AcOEt—light petroleum, 1 : 3). The reaction reached
completion within 10 min at 5—10 °C, the yield of FCO 2
was 72%.
The reaction of the Oꢀmethylated nitramine 4 with
93% H2SO4 also leads to FCO 2 (25 °C, 10 min, the yield
was 75%). This reaction presumably also proceeds through
the intermediate oxodiazonium ion, which is formed as
a result of protonation of the N=N(O)—OMe group and
subsequent elimination of methanol (see Scheme 3). The
detailed mechanism of this reaction, including quantum
chemical calculations, has been considered by us earlier9
for the synthesis of furazanocinnolineꢀ5ꢀoxide 1 as an exꢀ
ample (see Scheme 1).
Compounds 4, 6, and 7 were characterized by 1H, 13C,
and 14N NMR spectra. 14N NMR spectra are especially
informative, which exhibit sharp signals for the nitro groups
of the salt 7 (acetoneꢀd6, δN –13, Δν1/2 = 55 Hz) and
nitramine 6 (CDCl3, δN –36) and somewhat broad signal
for the diazenoxide group N→O in the compound 4
Nitration of FCO 2 with the conc. HNO3/H2SO4 mixꢀ
ture resulted in the 7ꢀnitroꢀsubstituted compound 9 in 75%
yield, which, like compound 2, is a potential NOꢀdonor
(Scheme 4).

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Russ.Chem.Bull., Int.Ed., Vol. 60, No. 10, October, 2011
Zelenov et al.
Scheme 3
Scheme 4
heating at 150—160 °C for 4 h in benzonitrile or without
solvent (Scheme 5).
Scheme 5
The structures of FCO 2 and 9 were confirmed by 1H,
13C, and 14N NMR spectroscopic data. The 14N NMR
spectra of these compounds exhibit sharp signals for the
N(5) atoms of the azoxy group and broad signals for the
N(1) atoms of the furoxane ring,4a whereas the spectrum
of compound 9 additionally contains a signal for the NO2
group (Table 1).
Table 1. The 1H and 14N NMR spectra of cinnolinofuroxaꢀ
nes 2 and 9
Peaks of the molecular ions and the fragment ions
[M – NO]+ and [M – 2 NO]+ characteristic of furoxanes4b
are observed in the mass spectra of FCO 2 and 9.
Comꢀ
pound
1H NMR
(DMSOꢀd6, δ, J/Hz)
14N NMR
(acetoneꢀd6, δ, Δν1/2/Hz)
The 13C—1H correlations (HMBC and HSQC) were
used to assign signals in the 13C NMR spectra, which
unambiguously indicate that the Nꢀoxide oxygen atom of the
furoxane ring is in the neighborhood of the phenyl ring.
The 13C NMR spectra of compounds 2 and 9 are specificalꢀ
ly characterized by broadening of the signals for the C(5a)
atoms bound to the fragment N→O of the azoxy group. In
compound 9, the signal for the C(7) atom bound to the
NO2 group is also broadened. An upfield shift of the signal
for the C(9b) atom bound to the fragment N→O of the
furoxanes ring is also typical of both compounds.4c
Compounds 2 and 9 exist as one isomer. Cinnolinoꢀ
furoxane 2 does not isomerize giving compound 2´ on
2
8.01 (ddd, 1 Н, Н(7),
J = 8.7, J = 7.9, J = 1.4);
8.15 (td, 1 Н, Н(8),
J = 7.9, J = 1.0);
8.34 (dd, 1 Н, Н(9),
J = 7.9, J = 1.4);
–22 (N(1)
furoxane,
Δν1/2 = 500);
–50 (N(O)=N,
Δν1/2 = 15)
8.54 (dd, 1 Н, Н(6),
J = 8.7, J = 1.0)
9
8.58 (d, 1 Н, Н(9),
J = 8.6);
8.88 (dd, 1 Н, Н(8));
9.09 (d, 1 Н, Н(6), J = 2.0)
–54 (N(O)=N,
Δν1/2 = 20);
–19 (NO2,
Δν1/2 = 110)*
* The signal for the Nꢀoxide nitrogen atom of the furoxane ring
is overlapped with the signal for the nitro group.

Oxodiazonium ion generation
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 10, October, 2011
2049
Table 2. The 13C NMR spectraa,b of cinnolinofuroxanes 2 and 9
Comꢀ
pound
δ
С(3a)
С(5a)
C(6)
C(7)
C(8)
C(9)
C(9a)
С(9b)
2
9
156.5
156.5
139.7 (br.s)
139.8 (br.s)
122.9
118.2 (br.s)
132.9
149.0
135.6
129.6
123.0
124.8
116.5
121.6
100.6 (br.s)
100.5
a In DMSOꢀd6.
b The signals were assigned using the 2 D 13C—1H NMR spectra (HMBC and HSQC).
added dropwise to a solution of crude Naꢀsalt 7 (74 mg) in AcOEt
(20 mL) at –40 °C, inorganic salts were rapidly separated by
filtration. A solution of NaOH (80 mg) in anhydrous MeOH (2 mL)
was added dropwise to a solution of nitramine 3 at –30 °C (to pH 7).
After the solvents were evaporated in vacuo, the residue (67 mg)
was crystallized (AcOEt (6 mL) and Et2O (12 mL)) to obtain
Naꢀsalt 7 (51 mg) as white crystals, which start to decomꢀ
pose about 230 °C. Found (%): C, 39.57; H, 1.98; N, 22.67.
C8H5N4NaO4. Calculated (%): C, 39.36; H, 2.06; N, 22.95. IR
(KBr), ν/cm–1: 1636 s, 1612 s, 1601 s, 1484 w, 1436 s, 1388 s,
1340 s, 1312 s. 1H NMR (acetoneꢀd6), δ: 7.44—7.51 (m, 3 H,
H(3´), H(4´), H(5´)); 8.17 (d, 2 H, H(2´), H(6´), J = 8.1 Hz).
13C NMR (acetoneꢀd6), δ: 111.9 (C(3)); 125.6 (C(1´)); 128.0
(C(2´), C(6´)); 129.4 (C(3´), C(5´)); 130.7 (C(4´)); 159.8 (C(4)).
14N NMR (acetoneꢀd6), δ: –13 (NO2, Δν1/2 = 55 Hz).
4ꢀ[Methoxy(oxido)diazenyl]ꢀ3ꢀphenylꢀ1,2,5ꢀoxadiazoleꢀ2ꢀ
oxide (4) and 4ꢀ[Nꢀmethylꢀ(Nꢀnitro)amino]ꢀ3ꢀphenylꢀ1,2,5ꢀoxaꢀ
diazoleꢀ2ꢀoxide (6). A solution of diazomethane in diethyl ether
obtained from Nꢀmethylnitrosourea (380 mg, 3.7 mmol) was
added to a stirred solution of nitramine 3 in diethyl ether obꢀ
tained by method A and after the drying agent was removed at
5 °C. After 5 min, Et2O was evaporated in vacuo to obtain
a mixture of isomers (201 mg), which was separated by preparaꢀ
tive TLC (benzene) to give Oꢀmethyl compound 4 (67 mg, 28%)
and Nꢀmethyl compound 6 (51 mg, 22%).
Experimental
1
H, 13C, and 14N NMR spectra were recorded on a Bruker
DRXꢀ500 spectrometer (500.13, 125.76, and 36.14 MHz, reꢀ
spectively). Chemical shifts are given relative to Me4Si (1H, 13C)
or MeNO2 (14N, external standard, the highꢀfield chemical shifts
are negative). IR spectra were recorded on a Specord Mꢀ80
spectrometer. Mass spectra were recorded on a Kratos MSꢀ300
instrument (EI, 70 eV). Reaction progress was monitored using
thinꢀlayer chromatography (Merck 60 F254). Silica gel was used
for column chromatography. A solution of diazomethane in diꢀ
ethyl ether11 and 4ꢀaminoꢀ3ꢀphenylfuroxane (5) (see Ref. 12)
were obtained according to the known procedures.
4ꢀNitraminoꢀ3ꢀphenylfuroxane (3). A. 4ꢀAminoꢀ3ꢀphenylꢀ
furoxane (5) (0.18 g, 1 mmol) was added to a nitrating mixture
(2.68 g, containing HNO3 (1.88 g, 29.9 mmol), NH4NO3 (0.52 g,
6.5 mmol), and H2O (0.28 g)) with stirring at 8 °C. The reaction
mixture was stirred for 1 h at 10 °C, then poured on finely crushed
ice (20 g). The aqueous solution was rapidly extracted with Et2O
(3×10 mL). The organic layers were washed with cold water
(2×3 mL) and dried with MgSO4 in refrigerator for 1 h periodiꢀ
cally shaking the mixture, then the drying agent was filtered off.
According to the TLC data (AcOEt—light petroleum, 1 : 3), the
solution contained nitramine 3, some amount of unreacted startꢀ
ing compound 5 and unidentified impurities.
Compound 4. M.p. 68—71 °C. Found (%): C, 45.89; H, 3.29;
N, 23.50. C9H8N4O4. Calculated (%): C, 45.77; H, 3.41;
B. 4ꢀAminoꢀ3ꢀphenylfuroxane (5) (0.18 g, 1 mmol) was addꢀ
ed to a nitrating mixture (3.58 g, containing HNO3 (2.42 g,
38.4 mmol), NH4NO3 (0.62 g, 7.7 mmol), and H2O (0.54 g))
with stirring at 25 °C (water bath). The reaction mixture was
stirred for 2 h at 25 °C. The subsequent treatment was similar to
that in method A.
1
N, 23.72. H NMR (CDCl3), δ: 4.18 (s, 3 H, CH3); 7.48—7.53
(m, 3 H, H(3´), H(4´), H(5´)); 8.02 (d, 2 H, H(2´), H(6´),
J = 7.3 Hz). 13C NMR (CDCl3), δ: 58.7 (CH3); 110.1 (C(3));
121.8 (C(1´)); 127.3 (C(2´), C(6´)); 128.9 (C(3´), C(5´)); 130.8
(C(4´)); 153.7 (C(4)). 14N NMR (CDCl3), δ: –52 (=N(O),
Δν1/2 = 140 Hz).
4ꢀNitraminoꢀ3ꢀphenylfuroxane Naꢀsalt (7). A solution of
NaOH (80 mg, 2 mmol) in anhydrous MeOH (2 mL) was added
dropwise to the solution of nitramine 3 in diethyl ether obtained
by method A with stirring; temperature was maintained from
–10 to –12 °C, pH was control using indicator paper. The addiꢀ
tion of the NaOH solution was stopped when the pH reached 7
(the solution turned its color from yellow to orange), a precipiꢀ
tate was filtered off, washed with Et2O (2×5 mL), and dried in
air. A solid residue was obtained (270 mg), which was the Naꢀsalt
of nitramine 7 with impurities of other salts. To remove NaNO3,
the salt 7 was dissolved on a filter in the AcOEt : MeOH = 5 : 1
mixture (4×5 mL). After the solvents were evaporated in vacuo,
Naꢀsalt 7 (184 mg, 76%) was obtained. This substance begins to
decompose without melting at 160 °C. It was used for the synꢀ
thesis of FCO 2 without additional purification.
Compound 6. M.p. 76—79 °C. Found (%): C, 45.82; H, 3.33;
N, 23.45. C9H8N4O4. Calculated (%): C, 45.77; H, 3.41;
1
N, 23.72. H NMR (CDCl3), δ: 3.86 (s, 3 H, CH3); 7.50—7.53
(m, 3 H, H(3´), H(4´), H(5´)); 7.71—7.74 (m, 2 H, H(2´), H(6´)).
13C NMR (CDCl3), δ: 39.7 (CH3); 111.3 (C(3)); 121.5 (C(1´));
126.2 (C(2´), C(6´)); 129.4 (C(3´), C(5´)); 131.3 (C(4´)); 152.1
(C(4)). 14N NMR (CDCl3), δ: –36 (NO2, Δν1/2 = 35 Hz).
[1,2,5]Oxadiazolo[3,4ꢀc]cinnolineꢀ1,5ꢀdioxide (2). A. A freshꢀ
ly prepared and cooled (to 0 °C) solution of HNO3 (38 mg,
0.6 mmol) (d = 1.5 g cm–3) in Ac2O (1 mL) was added to
a suspension of compound 5 (107 mg, 0.6 mmol) in Ac2O (1 mL)
at 5 °C with stirring, followed by addition of a solution of H2SO4
(60 mg, 0.6 mmol) (d = 1.83 g cm–3) in Ac2O (1.5 mL). After
10 min, the reaction mixture was poured into the water—ice
mixture (25 mL), stirred for 30 min to complete the hydrolysis of
Ac2O, a precipitate was filtered and dissolved in benzene (20 mL).
An analytical sample of Naꢀsalt 7 was obtained as follows.
A solution of H2SO4 (30 mg, 0.3 mmol) in AcOEt (3 mL) was

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Russ.Chem.Bull., Int.Ed., Vol. 60, No. 10, October, 2011
Zelenov et al.
The filtrate was extracted with benzene (10 mL). The comꢀ
bined organic extracts were dried with MgSO4, the solvent
was evaporated in vacuo to obtain crude product (126 mg).
Column chromatography (CHCl3) yielded compound 2 (89 mg,
72%) as yellow crystals, m.p. 203—204 °C (from CHCl3). After
crystallization from DMSO m.p. 206—207 °C. Found (%):
C, 47.23; H, 1.78; N, 27.24. C8H4N4O3. Calculated (%): C, 47.07;
H, 1.97; N, 27.44. IR (KBr), ν/cm–1: 1603 s, 1592 s, 1560 s,
1480 s, 1450 s, 1440 s, 1412 s, 1348 s, 1204 s, 1164 s. MS,
m/z (Irel (%)): 204 [M]+ (82), 174 [M – NO]+ (62), 144
[M – 2 NO]+ (100).
1392 w, 1348 s, 1276 m, 1248 m. MS, m/z: 249 [M]+, 219
[M – NO]+, 189 [M – 2 NO]+.
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 10ꢀ03ꢀ00752).
References
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B. Sulfuric acid (1 mL) was added in one portion to the
Oꢀmethylated nitramine 4 (10 mg, 0.045 mmol) at 25 °C with
vigorous stirring. The reaction mixture was kept at 25 °C for
10 min, poured into water with ice (3 mL), and extracted with
CH2Cl2 (5×3 mL). The organic extracts were combined, washed
with water (2 mL), dried with MgSO4, the solvent was evaporatꢀ
ed in vacuo. The yield of FCO 2 was 7 mg (75%). The compound
was identical to that obtained earlier.
C. A solution of H2SO4 (28 mg, 0.29 mmol) (d = 1.83 g cm–3
)
in Ac2O (1 mL) was added to a solution of Naꢀsalt 7 (34 mg,
0.14 mmol) in Ac2O (1 mL) at 5 °C with stirring. During addiꢀ
tion of H2SO4, the yellow reaction solution initially turned colorꢀ
less, but then acquired yellow color again. The reaction mixture
was stirred at 15 3 °C for 1.5 h, then poured in the water—ice
mixture (30 mL) and stirred for 30 min. A precipitate was filtered
off and dissolved in benzene (10 mL). The filtrate was extracted
with benzene (3×10 mL), the combined organic extracts were
dried with MgSO4, benzene was removed in vacuo to give
FCO 2 (25 mg, 89%), m.p. 199—203 °C, which was identical to
that obtained earlier.
7ꢀNitroꢀ[1,2,5]oxadiazolo[3,4ꢀc]cinnolineꢀ1,5ꢀdioxide (9).
Furoxanocinnolineꢀ5ꢀoxide 2 (80 mg, 0.39 mmol) was added to
a mixture of HNO3 (3 mL) (d = 1.5 g cm–3) and H2SO4 (2 mL)
(d = 1.83 g cm–3) at 5 °C. The reaction mixture was stirred
at 22—23 °C for 1 h, poured into ice (50 g), and extracted
with AcOEt (4×10 mL). The combined organic extracts were
washed with H2O (3×5 mL), dried with MgSO4, and the solvent
was evaporated in vacuo to obtain FCO 9 (73 mg, 75%) as bright
yellow crystals, m.p. 181—187 °C. After crystallization
from AcOEt, pure FCO 9 (57 mg, 58%) was obtained,
m.p. 186—188.5 °C. Found (%): C, 38.65; H, 1.20; N, 28.05.
C8H3N5O5. Calculated (%): C, 38.57; H, 1.21; N, 28.11. IR
(KBr), ν/cm–1: 1652 s, 1620 m, 1608 s, 1532 s, 1488 s, 1428 s,
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1935, p. 3.
12. A. R. Gagneux, R. Meier, Helv. Chim. Acta, 1970, 53, 1883.
Received March 1, 2011;
in revised form September 20, 2011